The present invention relates generally to an optical assembly. More particularly, the invention relates to a film assembly for use in a display system.
Some optical display systems include a film designed to increase the amount of on-axis brightness of the optical display system by redirecting off-axis light and recycling the on-axis light such that it eventually emerges from the display as on-axis light. For example, the 3M brand BRIGHTNESS ENHANCEMENT FILM (BEF) available from 3M Company of St. Paul, Minn. is one type of optical film that can be used to enhance optical display systems. BEF and similar films typically include an array of prisms on one surface that are large in comparison with the wavelength of light. These structures increase the amount of light that is directed toward a viewer. In use, these films typically increase on-axis illumination at the expense of off-axis illumination in one or two dimensions. In this fashion, the material can help the display designer achieve the desired amount of on-axis illumination with reduced power consumption. Various embodiments of BEF and other similar films having structured surfaces are described in, e.g., U.S. Pat. No. 5,394,255 (Yokota et al.); U.S. Pat. No. 5,552,907 (Yokota et al.); U.S. Pat. No. 6,052,164 (Cobb, Jr. et al.); U.S. Pat. No. 6,091,547 (Gardiner et al.); and U.S. Pat. No. 6,111,696 (Allen et al.).
Brightness enhancement may be achieved with such prismatic structured surface films through a process of reflection and refraction that preferably includes light recycling. When used in preferred backlight configurations, prismatic structured surface films help to direct light toward the viewer (usually positioned directly in front of the display system) that would otherwise leave the screen at a high angle, missing the viewer.
Improvements in display brightness, uniformity, and overall performance are continually being sought, and brightness enhancement films and prism structures are often utilized in liquid crystal displays.
Liquid crystal displays (LCDs) are optical displays used in devices such as laptop computers, hand-held calculators, digital watches and televisions. Some LCDs include a light source that is located to the side of the display, with a light guide positioned to guide the light from the light source to the back of the LCD panel. Other LCDs, for example some LCD monitors and LCD televisions (LCD-TVs), are directly illuminated using a number of light sources positioned behind the LCD panel. This arrangement is increasingly common with larger displays, because the light power requirements, to achieve a certain level of display brightness, increase with the square of the display size, whereas the available real estate for locating light sources along the side of the display only increases linearly with display size. In addition, some LCD applications, such as LCD-TVs, require that the display be bright enough to be viewed from a greater distance than other applications, and the viewing angle requirements for LCD-TVs are generally different from those for LCD monitors and hand-held devices.
Some LCD monitors and most LCD-TVs are commonly illuminated from behind by a number of cold cathode fluorescent lamps (CCFLs). These light sources are often linear and typically extend across one entire dimension of the display, either in a parallel array or along an edge.